Anthracene derivatives bearing thiourea and glucopyranosyl groups for the highly selective chiral recognition of amino acids: opposite chiral selectivities from similar binding units.

Two new anthracene thiourea derivatives, 1 and 2, were investigated as fluorescent chemosensors for the chiral recognition of the two enantiomers of alpha-amino carboxylates. Especially, host 2 displayed K(L)/K(D) values as high as 10.4 with t-Boc alanine. Furthermore, the D/L selectivity of hosts 1 and 2 is opposite, even though both hosts bear the same glucopyranosyl units. These intriguing opposite D/L binding affinities by 1 and 2 were obtained without/with H-pi interaction between anthrancene moiety and the methyl groups, which were explained by extensive high-level theoretical investigations taking into account the dispersion energy as well as the 2D-NMR chemical shifts.

Extended application of a chiral stationary phase based on (+)-(1 8-crown-6)-2,3,11,12-tetracarboxylic acid to the resolution of N-(substituted benzoyl)-alpha-amino acid amides.

A chiral stationary phase (CSP 1) based on (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid was applied to the resolution of N-(substituted benzoyl)-alpha-amino acid amides and esters. N-(Substituted benzoyl)-alpha-amino acid amides were well resolved using a mixture of acetic acid-triethylamine-acetonitrile (0.01:0.05:100, v/v/v) as an optimum mobile phase while N-(substituted benzoyl)-alpha-amino acid esters were not resolved at all. In contrast, both N-(substituted benzoyl)-alpha-amino acid amides and esters were not resolved at all or resolved very poorly on another CSP (CSP 2), which lacks the two N-H hydrogens of the amide tethers of CSP 1. Among the substituents on the benzoyl group of analytes, the nitro group was the best for good resolution of analytes on CSP 1. From these results, the two N-H hydrogens of the amide tethers of CSP 1, the carbonyl oxygen of the amide group of analytes, and the nitro group on the benzoyl group of analytes were concluded to play significant roles in chiral recognition. In addition, various N-(3,5-dinitrobenzoyl)leucine amides with different lengths of N-alkylamide chains were resolved on CSP 1 and N-(3,5-dinitrobenzoyl) leucine N-propylamide was found to show the best chiral recognition in terms of the separation (alpha = 1.30) and the resolution factor (Rs= 3.17).

Unusual resolution of N-(3,5-dinitrobenzoyl)-alpha-amino acids on a chiral stationary phase based on (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid.

While HPLC chiral stationary phases (CSPs) based on chiral crown ethers have been known useful for the resolution of only racemic primary amino compounds or some secondary amino compounds, in this study, we first demonstrated that the CSP based on (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid is also useful for the resolution of N-benzoyl-alpha-amino acids, which do not contain a primary or secondary amino group. Especially, N-(3,5-dinitrobenzoyl)-alpha-amino acids were resolved better than corresponding N-(3-nitrobenzoyl)- or N-benzoyl-alpha-amino acids, the separation (alpha) and the resolution factors (R(S)) for the resolution of eight N-(3,5-dinitrobenzoyl)-alpha-amino acids being in the range of 1.06-1.81 and 0.54-2.81, respectively. The optimum mobile phase condition was the mixture of acetic acid-triethylamine-acetonitrile with the ratio of 0.05/0.25/100 (v/v/v).